The present invention relates to a screw-type compressor with a motor driven and dry operating compressor unit having a suction side and a pressure side, whereby the suction side is connected to an intake line with a throttle or butterfly valve, which is located inside the intake line and can be displaced mechanically by means of an adjustment cylinder, whereby the pressure side is coupled to an outwardly extending pressure line, which, for the supply of the compressed air, and through the intermediary of a check valve, is connected to a compressed air system, and whereby the pressure line is connected to an air relief valve via an air relief line for the relief of pressure during idling operation of the compressor unit as a result of the butterfly valve being located in a position allowing only a small cross-sectional opening area or as a result of the butterfly valve being located in a completely closed position.
Screw-type compressors in general have the problem that, in the case of a displacement of the butterfly valve into its closed position, depending on the inherently present pressure in the associated compressed air system that is to be supplied, the difference in pressure between the suction side and the pressure side of the compressor unit increases continuously, so that the compression output that is to be performed by the compressor unit increases correspondingly. In screw-type compressors that are configured with an oil-flooded compressor unit, the thereby resulting increased heat is dissipated via the lubricating oil circuit of the compressor unit. In oil-free or, in other words, dry operating compressor units, the pressure side of the compressor unit is relieved, during idling operation of the aforementioned kind, by means of a correspondingly located air relief valve. The development of a difference in pressure is hence prevented so that, during the idling operation, the compressor unit does not work against the inherently present pressure on the pressure side and, hence, no additional heat stress results.
A screw-type compressor of the aforementioned kind is known from use according to the brochure “Stationary oil-free screw-type compressors; the T-series, dual stage, T60Z through T240Z” by ECOAIR from May 1996. In that screw-type compressor, the actuation of the butterfly valve that is located in the intake line is realized by means of an associated adjustment cylinder, which is acted upon by the oil pressure that serves for lubricating the bearing of the compression unit. The provided air relief valve is mechanically coupled to the adjustment cylinder or, respectively, to the displacement of the butterfly valve, resulting in a forced synchronization of the position of the butterfly valve and the opening state of the air relief valve.
Associated with the known structural configuration is the disadvantage that, due to the mechanically realizable surface conditions, the mechanical actuation of the air relief valve requires significantly higher actuating forces and therefore higher oil pressures than necessary or present for the lubrication of the compressor unit. Furthermore, an adaptation of the air relief to single or dual stage compressor units is only possible by using different and distinct mechanical components. Finally, due to the high temperature of the compressed medium, preferably a gas at approximately 200 to 240° Celsius, and therefore the necessity to use specific materials or, respectively, coatings, the expenditure for the manufacturing of the mechanical configuration is correspondingly high.
It is therefore an object of the present application to make the actuation of the air relief valve on a screw-type compressor of the aforementioned kind easier and more expedient.